1. Field of the Invention
This invention relates to photography, and more particularly, it relates to photographic processes performed in ambient light and to photographic products useful in such processes.
2. Description of the Prior Art
A number of diffusion transfer processes for producing photographic images in both black-and-white and in color are now well known. Of particular interest are diffusion transfer processes wherein the image-receiving layer carrying the transfer image is not separated from the developed photosensitive layer(s) after processing but both components are retained together as a permanent laminate. Included as part of the laminate is a layer of a light-reflecting material, preferably titanium dioxide, positioned between the image-carrying layer and the developed photosensitive layer(s). The light-reflecting layer separating the image-carrying and photosensitive components provides a white background for the transfer image and masks the developed photosensitive layer(s). In addition to these layers, the laminate usually includes dimensionally stable outer layers or supports, at least one of which is transparent so that the resulting transfer image may be viewed by reflection against the background provided by the light-reflecting layer. Diffusion transfer processes for forming images viewable without separation of the photosensitive and image-receiving components and film units useful in such processes are described, for example, in U.S. Pat. Nos. 3,415,644, 3,415,645 and 3,415,646 issued Dec. 10, 1968 to Edwin H. Land.
U.S. Pat. No. 3,647,437 issued Mar. 7, 1972 to Edwin H. Land also is concerned with diffusion transfer processes wherein the resulting photograph comprises the developed photosensitive layer(s) retained with the image-receiving layer as part of a permanent laminate. In the processes disclosed in this patent, a photographic film unit comprising a photosensitive element is developed in ambient light but further undesired exposure during processing is prevented by a light-absorbing material or optical filter agent which is retained in the processed film unit. In a preferred embodiment, the optical filter agent is a pH-sensitive dye, i.e., a dye possessing spectral absorption characteristics that are reversibly alterable in response to changes in environmental pH and particularly, a pH-sensitive dye having a colored or light-absorbing form above a given alkaline pH and a colorless or non-light-absorbing form below said pH. In a particularly preferred embodiment, the film unit is of the type described in aforementioned U.S. Pat. No. 3,415,644 and comprises a first sheet-like component comprising an opaque support carrying a silver halide emulsion layer(s) and a second sheet-like component comprising a transparent support carrying an image-receiving layer which are in fixed relationship prior to exposure, which relationship is maintained after processing. After photoexposure through said transparent support, an aqueous alkaline processing composition is distributed in a thin layer between said components. The processing composition contains a light-reflecting pigment and at least one pH-sensitive dye which is in its colored form at the initial pH of said aqueous alkaline processing composition and which, after at least the initial stages of processing, is converted to its colorless form by reducing the environmental pH, for example, by including an acid-reacting layer as part of the film unit. The concentrations of the light-reflecting pigment and light-absorbing optical filter agent required to provide adequate protection of the photosensitive layer(s) will vary with the process being performed and the anticipated conditions, e.g., light intensity, dark time, etc. Preferably, the concentrations of these materials are such that the processing composition layer containing the pigment and optical filter agent will have a transmission density of at least about 6 but a reflection density not greater than about 1.
Various pH-sensitive dyes have been disclosed as light-absorbing optical filter agents for protecting a selectively exposed photosensitive material from post-exposure fogging in the presence of extraneous incident light. Examples of pH-sensitive dyes that have been found particularly useful are the phthaleins, i.e., the phthalide and naphthalide dyes derived from 1-naphthols disclosed in U.S. Pat. No. 3,702,245 issued Nov. 7, 1972 to Myron S. Simon and David P. Waller and the phthalide and naphthalide dyes derived from indoles disclosed in U.S. Pat. No. 3,702,244 issued Nov. 7, 1972 to Stanley M. Bloom, Alan L. Borror, Paul S. Huyffer and Paul T. MacGregor. As discussed in the latter patent, indole phthaleins especially useful for photographic processes employing highly alkaline media are those containing a 2-ortho-hydroxyphenylindol-3-yl radical and a second indol-3-yl radical substituted in the 7-position with, for example, carboxy, sulfonamido or sulfamoyl or a second indol-3-yl radical substituted in the 5-position with an electronwithdrawing group, for example, carboxy or cyano and indole phthaleins containing a 7-carboxy-indol-3-yl radical and a second indol-3-yl radical substituted in the 7-position with, for example, sulfonamido or sulfamoyl. As discussed in these and other patents, a combination of the indole and 1-naphthol phthaleins generally are used where it is desired to provide protection from post-exposure fogging throughout the visible spectrum.
U.S. Pat. No. 4,456,674 issued June 26, 1984 to Leon D. Cerankowski, Gary S. LaPointe and Neil C. Mattucci discloses enhanced opacification systems employing metal cations for complexing with the phthalein optical filter agents and in one embodiment discloses the use of certain bivalent transition metal cations, such as, zinc and cadmium for complexing with the carboxyindole phthalein to increase opacification in the green region of the visible spectrum (500-600 nm). Presumably, these bivalent metal cations bind with the indole nitrogen of the carboxyindole phthalein to produce a spectral shift in dye .lambda..sub.max from the mid-400 nm range to over 500 nm thereby increasing the transmission density of the pigmented processing composition layer in the spectral region where opacification failures first manifest themselves due to thin spots in reagent spreading or using lesser quantities of processing composition, i.e., thinner layers of reagent.